Missing cables, sticky controllers, not breaking a 50 to buy a console; those are just some of the joys that op-shopping as to offer.
Generally speaking, I don't have much luck when it comes to buying consoles from op-shops. Usually you only find a handful of CD based 90's games among $2 jackets and 50 cent plates, but there is a particular Good Sammy's I know where I bought this Xbox for $30. This is actually the same Good Sammy's where I bought my Nintendo 64 from, so at the moment my opinion on that particular storefront is quite high.
$30 bought me the console, two controllers and a power cable. Sadly, one of the controllers is after market, and the legitimately branded one is missing the part of the cable that is suppose to stop cable breaks. Good idea in theory, but I guess those end bits are easy to loose.
Unfortunately the after market controller I can plug in is quite sticky. It doesn't seem to be anything sickly (Coke maybe?) but it's still putting me off playing on the console for an extended amount of time until I can find a replacement for the end of that cable.
I have played it long enough to know it works though, and I bought Project Gotham Racing from a thrift store for $4 (which seems quite fun from the little I've played). As for the missing audio/video cable, I'm currently borrowing one off a friend. There is an after market replacement coming in the mail though.
While I don't think I can class the original Xbox as 'retro' yet, it is now in that period of time where the hardware and software is insanely cheap. Considering the Xbox One has just been announced, it's nearly two generations behind now; so it's well on its way.
I should have a five to ten year gap where I can enjoy these prices (which I'm also doing with the PS2 at the moment) so there are fun, cheap times ahead.